Rotary winged aircraft or helicopters as they are more common known typically include a plurality of wings or blades commonly referred to as rotors which rotate about a shaft or mast. Such aircraft also include propulsion means such as a jet engine for rotating the rotors.
Helicopters have also been powered by the thrust of ram jets which are located at the tips of rotors or blades. For example, a Hiller Model H-J Hornet, a small two-place ram jet powered helicopter became the first ram jet powered unit to be certified in the United States and also the first C.A.A. approved tip mounted power plant for helicopters.
However, the use of tip mounted ram jets has not proven to be very useful because the ram jets are inefficient at the speeds that can be achieved at the tip of the rotor or blade. Both from a strength standpoint and from a shock wave standpoint, the speed is limited. The problem is that the ram compressor is less than the impact pressure because the airflow is not stopped (as it would be on impact), but instead can only be slowed down to the velocity needed to support the flame and exhaust velocity that gives thrust to the jet.
Another approach to a turbine engine which is mounted at the tip ends of helicopter rotor blades is disclosed in the U.S. patent of R. K. Grove No. 2,843,210. As disclosed therein, an angle mounted tip engine for aircraft sustaining rotors includes a vertical shafted power mechanism. The axis of th e vertical power shaft inclines slightly forward in terms of its translatory direction of orbital motion. The angle mounted tip engine also includes vertically spaced apart compressor and turbine members wherein the turbine member includes hollow stator vanes which are cooled by a stream of air conducted by a U-shaped conduit which bleeds off compressed air from the compressor member.
A more recent development is disclosed in my allowed copending application Ser. No. 08/939,715 entitled Helicopter Rotor Tip Jet. In that application, a helicopter includes a rotary wing and a ram jet engine mounted at the outer tip of the rotor for propelling the rotor a round the mast. The rotor or rotary wing also includes air inlet means at a distance from its tip and means for directing a flow of air which is subjected to centrifugal force through the rotor and into the ram jet engine to thereby increase the thrust of the ram jet engine.
It is presently believed that there may be a commercial market for an improved propulsion system in accordance with the present invention. There may be a commercial demand for such systems for use as a tip mounted gas turbine engine for a helicopter. The engine in accordance with the present invention are believed to be of relatively compact size with a relatively shallow aerodynamic design.
In addition, the propulsion system or engine in accordance with the present invention incorporates a vertically shafted power mechanism with one or more coaxial compressors and turbine sections and are constructed and arranged in a manner which should minimize any twisting moment on the rotor blade.